1. Field of the Invention
The present invention relates to a display apparatus, and in particular to a display apparatus in which a coloring phenomenon of a panel glass due to irradiation of electron beams is controlled.
2. Description of the Related Art
As a display apparatus, for example, there is a projection television apparatus using projection cathode ray tubes. In the projection television apparatus, three projection cathode ray tubes for a green image, a blue image, and a red image are arranged in positions a predetermined distance apart from a projection screen and reproduced images, which are displayed on face plates of the three projection cathode ray tubes, are superimposed one on top of another on a projection screen through a projection lens to display a color image.
The projection cathode ray tube of this type includes a vacuum envelope of glass. The vacuum envelope includes a panel section having a face plate, a cylindrical neck section having an electron gun housed therein, and a funnel section connecting the panel section and the neck section.
The projection cathode ray tube has a phosphor layer on an inner surface of the face plate of the panel section. High density electron beams emitted from the electron gun are deflected by vertical and horizontal deflection magnetic fields formed by deflection yokes to two-dimensionally scan the surface of the phosphor layer. Light generated by collision of the electron beams against phosphors is expanded and projected on the projection screen by the projection lens.
In the projection cathode ray tube of this type, when high density electron beams are projected on a fluorescent film, some electron beams do not hit phosphor particles in the phosphor layer and do not contribute to light emission of the phosphors. In other words, the electron beams may collide against the face plate directly. Some electrons are transmitted through the phosphors while scattering among the phosphor particles and projected on the phase plate. Consequently, the face plate itself is tinged with brown when the electron beams are projected on the face plate. This is a phenomenon called browning.
The browning occurs in the face plate because a relatively large number of electrons, which do not contribute to light emission of the phosphor particles, are present in the electron beams and projected on the face plate as described above. Thus, it is difficult to obtain a projection cathode ray tube having a bright display image.
When such browning occurs in the face plate, the phase plate absorbs, in particular, light in green to blue regions. Therefore, the browning is a factor that prevents a prolonged life of a projection cathode ray tube for green and a projection cathode ray tube for blue.
Note that such browning occurs not only in the projection cathode ray tube but also cathode ray tubes of a field emission image display apparatus, a display monitor tube, a television receiver, and the like, a cathode ray tube that does not have a phosphor layer on an inner surface of a panel glass, a cathode ray tube that has a layer other than the phosphor layer, and the like.
JP-A-7-262932 discloses a technique for coping with this type of browning. JP-A-7-262932 discloses a cathode ray tube in which an oxide film, which does not contain alkali and does not contain ions that obtain substantial reducibility due to impact of electron beams, is formed between an inner surface of a face plate of a panel section and a phosphor layer, and this oxide film has a thickness sufficient for preventing electron beams from penetrating through the oxide film to reach the face plate and does not have a color that is so dark as to prevent desired color coordinate specifications.
JP-A-8-31344 discloses another technique for coping with the browning. JP-A-8-31344 discloses a funnel for a beam index cathode ray tube that is attached with a light-receiving element, which detects index light from an index stripe formed on a fluorescent surface on an inner surface of a face plate of a panel section, on an outer surface side thereof. The funnel for a beam index cathode ray tube consists of non-leaden glass containing 0.1 to 2 weight % of CeO2 and having an X-ray absorption coefficient of 28 cm−1 or more at a wavelength of 0.6 Å.
In the cathode ray tube described in JP-A-7-262932, an oxide layer with high durability against electron beams is formed on an inner surface of the face plate of the panel section, whereby occurrence of discoloration (browning) of the faceplate due to collision of high-energy electron beams is prevented. However, efficiency of use of electron beams is not improved.
In the funnel for a beam index cathode ray tube described in JP-A-8-31344, a glass material constituting the funnel is formed by mixing cerium oxide with high durability against electron beams therein, whereby decline in a light transmittance of a light-receiving window portion due to the browning phenomenon is prevented. However, as in the JP-A-7-262932, efficiency of use of electron beams is not improved.